November 11, 1918, marked the end of World War I. A century later, we recall the era and its music: On the Banks of Green Willow by slain British officer George Butterworth, Barber’s Adagio for Strings, John Williams WWI-era film score War Horse, a variety of “Tunes from the Trenches,” and Ravel’s Concerto for the Left Hand, written for a pianist who lost his right arm in battle. We can learn from this sad but hopeful era.